Lightning Labs released pi402, an open-source extension enabling AI coding agents to pay for their own inference costs using Bitcoin via the Lightning Network. Designed for Pi coding agents, the tool eliminates the need for account registration, API keys, or credit cards—agents simply view a price and pay a Lightning invoice to resume work. Built on the L402 protocol, pi402 combines HTTP 402 "Payment Required" responses with Lightning invoices for instant settlement upon payment. This enables per-token billing, where agents pay only for actual consumption. Sellers can accept payments through Aperture and Lightmeter tools without running Lightning nodes themselves; settlements are handled by Wavelength, an Ark-based wallet. Demo pricing stands at approximately $0.375 per million input tokens and $1.50 per million output tokens.